Experiments - Essentials of Chemical Education - page 124

Fig. 5.3 Laue's hypothesis to get diffraction patterns by an X-ray beam through crystals [ 6 ]
constant, standard potential, energy turnover, and rate constant identify the chemi-
cal reaction.
In present-day laboratories, substances and chemical reactions are described by
methods of the instrumental analytics: such as paper-, column- and thin-layer
chromatography, gas chromatography (GC), mass spectrometry (MS), combi-
nations of GC and MS, atomic absorption spectroscopy (AAS), infrared spectro-
scopy (IR), nuclear magnetic resonance spectroscopy (NMR), and X-ray structure
analysis.
The required large instruments are not only very expensive, but also need
supervision by specially qualified staff. Students become acquainted with the
large appliances during their laboratory practicals, while teachers and pupils can
inspect them during a visit at a department of chemistry. Smaller instruments that
show the method in a clear and didactically reduced way have been developed for
school lessons, for example an apparatus for gas chromatography by Wiederholt [ 7 ]
and one for X-ray structure analysis by Brockmeyer [ 8 ]. Corresponding model
experiments for gas chromatography (E5.1) and X-ray analysis (E5.2) may demon-
strate it.
Synthesis of new substances: Perhaps the oldest function of experimentation is
the trial-and-error approach for the production of substances, which cannot be
found in pure form in nature. Table 5.2 shows several substances with the approxi-
mate date of their first description according to Schwedt [ 9 ].